Recent developments of early cosmology, inflation and late-time accelerating universe, are centered around the cosmological constant. It would be ideal if the fine-tuned cosmological constant problem is solved together with important cosmological issues including inflation, dark energy and cold dark matter. We shall discuss a possible framework to achieve this goal based on scalar-tensor gravity incorporating con formal coupling. In the proposed model the cosmological constant is elevated to a dynamical variable that evolves with cosmic expansion, and the inflaton motion may realize slow-roll inflation towards a potential minimum of a spontaneously broken phase and late-time roll-down to the point of zero cosmological constant at the field infinity. The key for this behavior is spontaneous symmetry breaking at inflation and symmetry restoration at later epochs. We shall discuss how these are realized and its inevitable consequence: strong gravity effects in the early universe, implying stronger gravitational wave emission and black hole formation of primordial origin. Cold dark matter consists of spatially inhomogeneous modes generated from thermal medium, and clumps made of cold dark matter may gravitationally collapse into primordial black holes which may constitute a part of cold dark matter. This talk is based on recent works listed below.
References
[1] M. Yoshimura, “Dynamical relaxation of cosmological constant”, arXiv: 2204.10809 [hep-ph] (2022).
[2] M. Yoshimura, “Stronger gravity in the early universe”, arXiv: 2204.11384 [gr-qc] (2022).
[3] M. Yoshimura, “Bifurcated symmetry breaking in scalar-tensor gravity”, arXiv: 2112.02835v2 (2021);
Phys.Rev. D105, 083522 (2022).